The field of art to which the invention pertains relates to compound cylinder and piston assemblies for actuating telescopic spreader frames for the handling of cargo containers, and more particularly to such compound assemblies in a hydraulic system which together is adapted to actuate the spreader frame to predetermined fixed positions of full extension and retraction, and to one of a plurality of preselected fixed positions intermediate full extension and retraction.
The present invention, as applied herein to an exemplary embodiment, other applications of which will be apparent to persons skilled in the art, is concerned with a type of spreader frame capable of handling a variety of types and sizes of cargo containers which, as a complex of containers and container handling equipment in the transportation industry, has become to be known as "containerization".
Differences in cargo container length have necessitated either the use of individual spreader frames of different sizes or expansible spreader frames capable of adjustment to various lengths. The frames are usually used with van carrier type vehicles, lift trucks, and crane equipment capable of engaging and transporting by means of a spreader frame such cargo containers, e.g., at freight terminals at which the capability for receiving all available types and sizes of containers for delivery or forwarding further along respective routes of shipment is important. Differences in container lengths have been adapted to accommodate inevitable differences in the size of shipments, the size of carriers, and other factors, in order to contribute flexibility and economy to the handling of freight, particularly in view of standardization of the height and width of all such containers.
Various length containers are made by different manufacturers; for example, containers of 20, 30 and 40 ft. in length are made by one manufacturer, 20, 24 and 40 ft. containers are made by a second, and 20, 35 and 40 ft. containers are made by a third. One expansible spreader frame construction which is adapted to handle a variety of container lengths is covered in U.S. Pat. No. 3,874,719, granted Apr. 1, 1975.